Dessert Christopher, Long Andrew J, Safdi Benjamin R
Leinweber Center for Theoretical Physics, Department of Physics, University of Michigan, Ann Arbor, Michigan 48109, USA.
Berkeley Center for Theoretical Physics, University of California, Berkeley, California 94720, USA.
Phys Rev Lett. 2022 Feb 18;128(7):071102. doi: 10.1103/PhysRevLett.128.071102.
Axions with couplings g_{aγγ}∼few×10^{-11} GeV^{-1} to electromagnetism may resolve a number of astrophysical anomalies, such as unexpected ∼TeV transparency, anomalous stellar cooling, and x-ray excesses from nearby neutron stars. We show, however, that such axions are severely constrained by the nonobservation of x rays from the magnetic white dwarf (MWD) RE J0317-853 using ∼40 ks of data acquired from a dedicated observation with the Chandra X-ray Observatory. Axions may be produced in the core of the MWD through electron bremsstrahlung and then convert to x rays in the magnetosphere. The nonobservation of x rays constrains the axion-photon coupling to g_{aγγ}≲5.5×10^{-13}sqrt[C_{aγγ}/C_{aee}] GeV^{-1} at 95% confidence for axion masses m_{a}≲5×10^{-6} eV, with C_{aee} and C_{aγγ} the dimensionless coupling constants to electrons and photons. Considering that C_{aee} is generated from the renormalization group, our results robustly disfavor g_{aγγ}≳4.4×10^{-11} GeV^{-1} even for models with no ultraviolet contribution to C_{aee}.
